Shuttle-reversing means

ABSTRACT

A flat weaving machine comprises an electrically operable travelling-field race and a gripper-type shuttle, which is reciprocable along said race. Means are provided for reversing the movement of the shuttle at each end of said race. Said means comprise two energy-storing spring devices disposed at opposite ends of said race. Each of said energy-storing spring devices comprises a torsion bar, which extends in a plane that is normal to said race, and a radial stressing arm, which is connected to said torsion bar and has a free end. The torsion bar is adapted to be stressed by a pivotal movement of said stressing arm in a predetermined sense, to be in an unlocked condition when stressed, and to relax so as to impart to said stressing arm a pivotal movement in a sense opposite to said predetermined sense. Two buffer guides extend in the longitudinal direction of said race. Two buffers are provided, each of which is freely slidably guided by one of said buffer guides along the same and contacts the free end of one of said stressing arms and is engageable by said shuttle and adapted to transmit force from said shuttle to said stressing arm to impart to the same a pivotal movement in said predetermined sense. Two resilient stops are provided, each of which is adapted to be engaged by one of said buffers under the force transmitted to said buffer by the associated torsion bar through the stressing arm connected thereto.

United States Patent [191 Filter [111 3,842,868 [451 Oct. 22, 1974 1 4] SHUTTLE-REVERSING MEANS [75] Inventor: Walther Filter, Langenhagen,

Germany [73] Assignees: Vereinigte Osterreichische Eisen-und Stahlwerke-Alpine Montan Aktiengesellschaft, Vienna, Austria; Establissement Wanderfield & C0., Schaan, Liechtenstein 22 Filed: Sept. 7,1973

[21] App]. No.2 395,298

[30] Foreign Application Priority Data Primary Examiner-Henry S. Jaudon Attorney, Agent, or Firm-Kurt Kelman [5 7 ABSTRACT A flat weaving machine comprises an electrically operable travelling-field race and a gripper-type shuttle, which is reciprocable along said race. Means are provided for reversing the movement of the shuttle at each end of said race. Said means comprise two energy-storing spring devices disposed at opposite ends of said race. Each of said energy-storing spring devices comprises a torsion bar, which extends in a plane that is normal to said race, and a radial stressing arm, which is connected to said torsion bar and has a free end. The torsion bar is adapted to be stressed by a pivotal movement of said stressing arm in a predetermined sense, to be in an unlocked condition when stressed, and to relax so as to impart to said stressing arm a pivotal movement in a sense opposite to said predetermined sense. Two buffer guides extend in the longitudinal direction of said race. Two buffers are provided, each of which is freely slidably guided by one of said buffer guides along the same and contacts the free end of one of said stressing arms and is engageable by said shuttle and adapted to transmit force from said shuttle to said stressing arm to impart to the same a pivotal movement in said predetermined sense. Two resilient stops are provided, each of which is adapted to be engaged by one of said buffers under the force transmitted to said buffer by the associated torsion bar through the' stressing arm connected thereto. 1

10 Claims, 7 Drawing Figures 1 SHUTTLE-REVERSING MEANS This invention relates to apparatus for reversing the movement of a gripper-type shuttle of a fiat weaving machine, comprising an electrically operated travelling-field'race for the shuttle and two energy-storing spring devices, which are disposed at opposite ends of the shuttle race and adapted to be stressed by the shuttle through the intermediary of a buffer. To enable in flat weaving machines comprising an electrically operable travelling-field race for the shuttle a braking of the shuttle as it leaves the travelling-field race and a subsequent movement of the shuttle into the range of the travelling-field race, it has been proposed (German Patent Specification 93,775) to provide energy-storing spring devices, which are disposed at opposite ends of the shuttle race and have springs which are stressed by the shuttle as it leaves the shed and are locked in a stressed condition so that the new filling thread can be received by the shuttle while the latter is at rest. For the subsequent pick, the spring is unlocked and the spring force imparts to the shuttle an acceleration which causes the shuttle to move into the range of the travelling-field race so that the travelling field of said race can draw the shuttle further through the shed. The spring of the energy-storing spring device consists of a coil spring and as said spring is stressed it stores the kinetic energy of the arriving shuttle. Thereafter, the spring delivers the stored energy to the shuttle so that there is no need for additional drive means for returning the shuttle into the range of the travelling-field race when the shuttle has been braked. It would be desirable to impart to the shuttle by the energy-storing spring device such an acceleration that the shuttle when entering the travelling-field race is at a velocity which is approximately as high as that of the travelling field. In this case, a temperature rise of the shuttle and f the travelling-field race will be avoided and the energy requirement will be minimized. These requirements can be fulfilled by the known flat weaving machine only to a very small extent. The coil spring of the energystoring spring device is stressed by means of a spring bolt, which is engaged by the shuttle and said spring can be used only where the mass forces and velocities v are small. For this reason, that known arrangement cannot meet present-day requirements for progressively higher picking rates. An additional disadvantage resides in the relatively hard engagement of the shuttle with the spring bolt due to the fact that the buffer consists only of a leather washer and the resulting shock imposes a strong load on the several components so that the life and reliability. of the arrangement are much reduced. Owing to the hard engagement, a leaf spring must be provided, which forces the shuttle against the spring bolt when the spring has been stressed.

It has also been proposed to store the kinetic energy of the shuttle and to use the stored kinetic energy to drive the shuttle in the opposite direction. It is difficult, however, to arrest the shuttle with a minimum of friction by means of an energy-storing spring device and to return the stored energy to the shuttle with a minimum loss. Whereas known shuttle-driving means in looms comprise a separate stressing device for supplying additional energy to the energy-storing spring device (German Patent Specification 822,827), the disadvantages involved in these shuttle-driving means are such that they have not been successful in practice. To provide an economic design, an energy-storing spring device which can be stressed by the shuttle itself can be used only to reverse the movement of the shuttle, as is required in flat weaving machines having a travellingfield race.

In other known shuttle-driving means (Austrian Patent Specification 100,582), the shuttle is driven by drive rollers provided at opposite ends of the shuttle race. The shuttle is braked at each end of the race by an energy-storing spring device, which is stressed by the arriving shuttle and subsequently relaxes to push the shuttle back to the drive rollers. In that arrangement, the shuttle acts on a buffer, which is composed of several leather components and which is connected to a stressing arm for a coil spring so that the kinetic energy of the shuttle can be gradually transmitted to the coil spring. When the energy-storing spring device has been stressed by the shuttle, the stressing arm is locked in its stressed position by the shuttle itself, which is forced by a brake block against a brake bar. When this shuttle brake is released, the drive rollers are swung into the path of the shuttle and the stressing arm is released and under its spring bias forces the shuttle to the drive rollers so thatthe spring force of the resiliently deformed buffer is also utilized. It is the main object of this known energy-storing spring device to brake the shuttle and to store the kinetic energy only to such an extent that the shuttle can return to the drive rollers without need for additional energy. On the other hand, the movement of the shuttle cannot be reversed with a minimum of loss.

Shuttle-driving means are known (German Patent Specification 1,194,340, Swiss Patent Specification 473,925), which comprise energy-storing spring devices including a tprsopm bar which can exert a spring force that is sufficient for entirely driving the shuttle. These torsion bars are wound up by separate winding means rather than by the shuttle. These arrangements comprise a picking lever which is connected to the torsion bar and drives the shuttle as the torsion bar is relaxed. At the other end of the race, the shuttle which has thus been driven is arrested by shuttle-arresting buffers, which serve to bring the shuttle to a stop in a predetermined position with a minimum of shock and without a rebounding of the shuttle. For this purpose, known shuttle-arresting buffers (Austrian Patent Specification 251,505) comprise a hollow body of rubberelastic material and a stop plate, which carries a forwardly bulging cup spring. The kinetic energy of the spring is taken up first by the cup spring, which is compressed against the stop plate, and only thereafter is the kinetic energy of the shuttle transmitted to the hollow body, which is compressed so that the air enclosed therein is displaced through an adjustable valve. As a result, the kinetic energy of the shuttle is transmitted to successive elements of increasing mass so that the shuttle is arrested without a shock.

Another known buffer for the picking stick of a weaving machine (Swiss Patent Specification 503,135) comprises a resilient U-shaped member, which is convex toward the picking stick and serves to equalize the movement of the damping element and the picking stick in the direction of the longitudinal axis of the stick. Only when the U-shaped member engages the damping member is such equalization of movement prevented by the frictional forces which are effective.

Pickers which are guided on a picker spindle (British Patent Specification 23,308, German Patent Specification 93,871) are known to transmit the necessary acceleration of the picking stick to the shuttle. To reduce the shock load, these pickers have a damping member of leather, plastics material or the like, which is held in a rigid housing.

It is an object of the invention to improve an apparatus for reversing the movement of a gripper-type shuttle of the kind described first hereinbefore in such a manner that the shuttle is braked with a minimum of shock and the stored kinetic energy is returned to the shuttle with a minimum of loss so that a relatively small differential velocity results between travelling field and the shuttle which enters the travelling-field race.

This object is accomplished according to the invention in that the energy-storing spring device consists of a torsion bar that extends in a plane which is normal to the shuttle race and said torsion bar is unlocked when in a stressed condition and is provided with a radial stressing arm, and that the buffer engages the free end of the stressing arm and is freely slidably mounted in a guide in the direction of travel of the shuttle and in its position of rest is held by the stressing arm against a resilient stop. By means of the stressing arm, the torsion bar is braked by the arriving shuttle; when the torsion bar has completely braked the shuttle, the torsion bar returns the stored energy to the shuttle by means of the stressing arm. The buffer engages the free end of the stressing arm to prevent a shock engagement of the shuttle with the stressing arm. When the movement of the shuttle has been reversed, the energy-storing spring device holds the buffer in position of rest against the stop so that a shock between the buffer and the stressing arm will be avoided when the shuttle returns and is arrested once more. The guidance of the buffer in the direction of travel of the shuttle affords the advantage that the buffer is always in the same position relative to the shuttle during the reversal of movement and need not be rotated together with the stressing arm.

To provide an arrangement which operates with particularly little noise and without shock, it is a feature of the invention to mount the torsion bar within a vertical tube or the like, which is carried by a foundation which is separate from the machine frame. Because the foundation for the tube is separate from the machine frame, the braking forces are not transmitted to the machine frame but are taken up separately so that the shocks are keptfrom the machine frame as the main loads need not be taken up by the actual machine frame. The vertical arrangement of the tube for the torsion bar results in a very small space requirement for the apparatus according to the invention so that the desired length of the torsion rod may be freely selected.

A particularly simple design will be obtained in accordance with a feature of the invention which resides in that the buffer is guided by a longitudinally slotted tube, which receives a wheeled carriage, which is connected to the buffer by a carrier, which extends through the longitudinal slot of the tube. The wheeled carriage ensures a low-friction guidance of the buffer. The wheels of the carriage roll on the inside surface of the tube which encloses the wheeled carriage, and this tube provides not only guidance but also protection. The buffer is connected to the wheeled carriage by a carrier, which extends through the longitudinal slot of the tube, and said buffer protrudes into the path for the shuttle whereas the buffer-guiding means cannot adversely affect the shuttle motion] To enable an absorption of the kinetic energy of the shuttle with a minimum of shock, the kinetic energy must be transmitted to the buffer in steps. For this purpose, the buffer according to the invention has in a manner known per se a rigid housing, which is open at least toward the shuttle and contains a resilient damping member, which, as is also known per se, forms a stop surface that is engageable for a resilient U-shaped member which bulges toward the shuttle, said stop surface being complementary to the end face of the shuttle. As a result, the shuttle first strikes on the forwardly bulging U-shaped member of the buffer and com presses said U-shaped member against the stop surface of the damping member. The stop surface of the damping member is complementary to the end face of the shuttle so that the pressure which is applied by the shuttle to the U-shaped member and by the latter to the damping member is uniformly distributed over the damping member. As a result, the velocity of the buffer housing is gradually increased to the velocity of the shuttle because even when the shuttle has initially contacted the buffer the elastic deformation of the U- shaped spring member and the damping member permits of a movement of the shuttle relative to the buffer housing, which transmits the kinetic energy to the stressing arm of the torsion bar. The kinetic energy of the shuttle cannot act fully on the torsion rod until the resistance of the damping member to deformation corresponds to the force which is exerted by the shuttle on the buffer because under that condition the damping member cannot be deformed further and fully transmits the force to the buffer housing whereas no more force is required to deform the damping member.

To ensure that the damping member can be deformed as freely as possible, the housing of the buffer consists according to the invention of two spaced apart plates, which are connected by pins to form a cage, in which the clamping member is held. In this cage, the deformation of the clamping member is hardly restricted by walls which contact the damping member so that the entire kinetic energy is not transmitted by the pins to the plates of the housing until the damping member has been subjected to a relatively large deformation. To improve the extent of the elastic deformation of the damping member, the plates may be formed in accordance with the invention with apertures through which the damping member can extend as it is deformed. For the same purpose, a free space is left between at least one of the plates and that portion of the damping member which is adjacent to the U-shaped member.

To avoid frictional forces between the stressing arm and the buffer as far as possible, it is a feature of the invention that the housing of the buffer carries a roller which protrudes toward the stressing arm of the energy-storing spring device and has an axis that is parallel to the axis of the torsion bar. The exclusively pivotal movement of the stressing arm and the translational movement of the buffer result in a relative movement between the stressing arm and the buffer and this relative movement results in undesirably high losses due to friction in case of a sliding friction between the stressing arm and the buffer.

Finally it is a feature of the invention that the stressing arm of the energy-storing spring device carries at its free end a surface which is engageable by the roller and is inclined to the direction of movement of the buffer when the stressing arm is in position of rest. This measure ensures additionally a shock-free transmission of force to the stressing arm because only part of the force acting on the stressing arm tends to rotate the latter at the beginning of the stressing movement.

An embodiment of the invention is shown diagrammatically and by way of example on the accompanying drawings, in which FIG. 1 is a top plan view showing an energy-storing spring device according to the invention together with a buffer,

FIG. 2 is a partly sectional view showing the energystoring spring device,

FIG. 3 is a bottom view showing a buffer according to the invention,

FIG. 4 is a sectional view showing a buffer which is guided in a slotted tube,

FIG. 5 is a front elevation showing the buffer according to the invention,

FIG. 6 is a top plan view showing the stressing arm in position of rest in contact with the buffer, and

FIG. 7 is a perspective view of a generally conventional flat weaving machine structure having a race and energy-storing spring devices at opposite ends thereof.

The apparatus provided according to the invention for reversing the motion of a gripper-type shuttle 1 in a flat weaving machine comprises essentially two energy-storing spring devices 2 provided at respective ends of the shuttle race 25, and a buffer 3, which is freely movably guided in the direction of travel of the shuttle and arranged to be struck by the shuttle 1. The shuttle is driven by electrical travelling field 26.

The energy-storing spring device 2 according to the invention comprises a torsion bar 4, which is mounted within a vertical tube 5 which is carried by a foundation 6 that is separate from the machine frame. The torsion bar 4 is non-rotatably held at one end in a mounting block 7, which is screw-connected to the tube 5,and at the other hand in a stressing arm 8, which is firmly connected to a bushing 10, which receives the torsion bar and is rotatably mounted in a bearing block 9.

The buffer 3 engages the free end of the stressing arm 8 and is connected by a carrier 11 to a wheeled carriage 12, which is guided in a tube 13. The carrier 11 extends through a longitudinal slot 14 of the tube so that the buffer 3 protrudes into the path of the shuttle 1 whereas the means for guiding the buffers cannot obstruct the movement of the shuttle. The wheels 15 of the carriage 12 roll on the inside surface of the tube 13 so that the buffer is freely movably guided in the direction of movement of the shuttle. At its end facing the shuttle l, the wheeled carriage 12 is provided with a buffer member 16, by means of which the stressing arm 8 when in position of rest holds the wheeled carriage against a resilient stop.

The buffer 3 comprises a housing, which consists of two spaced apart plates 18, which are connected by pins 17 to form a cage, which contains a damping member 19. At its end facing the shuttle, the resilient damping member 19 has a stop face 20 which is engageable by a resilient U-shaped member 21, which is bulged toward the shuttle and is also mounted in the housing for the buffer. The stop surface 20 of the damping member 19 is complementary to the end face of the shuttle.

A roller 22 having an axis that is parallel to the axis of the torsion bar is mounted between the plates 18 and protrudes toward the stressing arm 8 of the energystoring spring device 2.

When the shuttle 1 leaving the travelling field race 26 reaches the buffer 3, which is in contact with the free end of the stressing arm 8, the resilient U-shaped member 21 is first compressed until it engages the stop surface 20 of the damping member 19. The force which is transmitted by the shuttle l to the buffer 3 now acts on the damping member 19, which under the action of this force is elastically deformed and transmits only part of the force through the pins 17 and plates 18 to the roller 22, which is forced against the stressing arm 8. Because the stop surface is complementary to the end face of the shuttle, a uniform distribution of the pressure applied to the damping member 19 is ensured so that the damping member 19 is uniformly stressed. The force which is gradually exerted by the shuttle 1 on the housing of the buffer 3 through the intermediary of the U- shaped member 21 and the damping member 19 will be fully transmitted to the stressing arm 8 when the resistance of the damping member 19 to deformation corre sponds to the force which is exerted by the shuttle on the clamping member. Owing to this gradual transmission of force, the shuttle is arrested without shock so that the stressing movement is applied to the energystoring spring device 2 without shock. As the shuttle 1 is braked, its kinetic energy is stored by the energystoring spring device which immediately thereafter relaxes to return the stored energy to the shuttle.

To enable the damping member 19 to be deformed as freely as possible, the plates 18 have apertures 23, through which the damping membercan extend as it is additionally deformed. Besides, wedge-shaped gaps are left between the plates 18 and that portion of the damping member 19 which faces the U-shaped member 21; this gap also increases the extent to which the damping member 19 can be deformed.

To ensure that the force of the moving shuttle can be transmitted by the buffer 3 to the stressing arm 8 without shock, the stressing arm is provided at its free end with a surface 24 which is engageable by the roller 22 and in the position of rest of the stressing arm 8 is inclined to the direction of movement of the buffer 3. FIG. 6 shows the stressing arm 8 in position of rest. It is apparent therefrom that at the beginning of the pivotal movement of the stressing arm only part of the force of the buffer moving in the direction indicated by the arrow can act to wind up the torsion bar so that the force is transmitted without shock also from the buffer 3 to the stressing arm 8.

Immediately after the braking of the shuttle l by the energy-storing spring device 2, the torsion spring relaxes to accelerate the shuttle 1 in the opposite direction so that the shuttle 1 enters the range of the travelling-field raceway 26. FIG. 1 shows the stressing arm 8 approximately at the time when the motion is reversed. For the sake of clearness, the guide tube 13, the wheeled carriage 12 and the carrier 11 have been omitted. It is apparent from FIG. 1 that the stressing arm 8 may be provided with a cam face with which the roller 22 of the buffer is in rolling contact and which ensures a desired transmission of force to the stressing arm as the torsion bar is stressed.

As can be seen in the perspective view of FIG. 7, continuously reciprocating shuttle will insert a filling thread in the shed at each movement and place it on the reed roller consisting of reed shaft 27 and discs 28 (see application Serial No. 395,293 of even date of which I am ajoint inventor). After the filling thread has been inserted, it will be beaten up against the fabric resting on support 29 by rotation of the reed roller. The fabric is removed over breast beam 30 supported on pedestal 35, 36.

What is claimed is:

1. In a flat weaving machine which comprises an electrically operable travelling-field race and a gripper-type shuttle, which is reciprocable along said race, the provision of means for reversing the movement of said shuttle at each end of said race, said means comprising two energy-storing spring devices disposed at opposite ends of said race, each of said energy-storing spring devices comprising a torsion bar, which extends in a plane that is normal to said race, and a radial stressing arm, which is connected to said torsion bar and has a free end, said torsion bar being adapted to be stressed by a pivotal movement of said stressing arm in a predetermined sense, to be in an unlocked condition when stressed, and to relax so as to impart to said stressing arm a pivotal movement in a sense opposite to said predetermined sense,

two buffer guides extending in the longitudinal direction of said race,

two buffers, each of which is freely slidably guided by one of said buffer guides along the same and contacts the free end of one of said stressing arms and is engageable by said shuttle and adapted to transmit force from said shuttle to said stressing arm to impart to the same a pivotal movement in said predetermined sense, and

two resilient stops, each of which is adapted to be engaged by one of said buffers under the force transmitted to said buffer by the associated torsion bar through the stressing arm connected thereto.

2. Reversing means as set forth in claim 1, in a flat weaving machine which comprises a machine frame, which reversing means comprise two vertical torsion bar guides, each of which contains one of said torsion bars, and

foundation means which carry said torsion bar guides and are separate from said machine frame.

3. Reversing means as set forth in claim 1, in which each of said torsion bar guides consists of a torsion bar guide tube.

4. Reversing means as set forth in claim I, in which each of said buffer guides consists of a tube having a longitudinal slot,

a wheeled carriage is contained in and movable along each of said tubes,

a carrier extends through each of said slots and connects one of said carriages to the associated buffer.

5. Reversing means as set forth in claim 1, in a flat weaving machine in which said shuttle has two opposite end faces and in which each of said buffers comprises a rigid housing which is open at least toward the shuttle,

a resilient damping member contained in said housing and formed with a stop surface, and

a resilient U-shaped member which is bulged toward said shuttle,

said stop face being complementary to the associated end face of said shuttle.

6. Reversing means as set forth in claim 5, in which each of said buffer housings comprises two spaced apart plates, which are connected by pins to form a cage in which said damping member is held.

7. Reversing means as set forth in claim 6, in which said plates are formed with apertures and said damping member is adapted to extend through said apertures as it is deformed.

8. Reversing means as set forth in claim 6, in which each of said damping members has a portion which is adjacent to the associated U-shaped member and spaced from atleast one of said plates.

9. Reversing means as set forth in claim 5, in which each buffer housing carries a roller, which protrudes toward the associated stressing arm and has an axis that is parallel to the axis of the associated torsion bar.

10. Reversing means as set forth in claim 9, in which each of said stressing arms has at its free end a surface that is engageable by the associated roller and said engageable surface is inclined to the longitudinal direction of said race when the associated buffer engages the associated resilient stop under the force transmitted to said buffer by the associated torsion bar through the stressing arm connected thereto. 

1. In a flat weaving machine which comprises an electrically operable travelling-field race and a gripper-type shuttle, which is reciprocable along said race, the provision of means for reversing the movement of said shuttle at each end of said race, said means comprising two energy-storing spring devices disposed at opposite ends of said race, each of said energy-storing spring devices comprising a torsion bar, which extends in a plane that is normal to said race, and a radial stressing arm, which is connected to said torsion bar and has a free end, said torsion bar being adapted to be stressed by a pivotal movement of said stressing arm in a predetermined sense, to be in an unlocked condition when stressed, and to relax so as to impart to said stressing arm a pivotal movement in a sense opposite to said predetermined sense, two buffer guides extending in the longitudinal direction of said race, two buffers, each of which is freely slidably guided by one of said buffer guides along the same and contacts the free end of one of said stressing arms and is engageable by said shuttle and adapted to transmit force from said shuttle to said stressing arm to impart to the same a pivotal movement in said predetermined sense, and two resilient stops, each of which is adapted to be engaged by one of said buffers under the force transmitted to said buffer by the associated torsion bar through the stressing arm connected thereto.
 2. Reversing means as set forth in claim 1, in a flat weaving machine which comprises a machine frame, which reversing means comprise two vertical torsion bar guides, each of which contains one of said torsion bars, and foundation means which carry said torsion bar guides and are separate from said machine frame.
 3. Reversing means as set forth in claim 1, in which each of said torsion bar guides consists of a torsion bar guide tube.
 4. Reversing means as set forth in claim 1, in which each of said buffer guides consists of a tube having a longitudinal slot, a wheeled carriage is contained in and movable along each of said tubes, a carrier extends through each of said slots and connects one of said carriages to the associated buffer.
 5. Reversing means as set forth in claim 1, in a flat weaving machine in which said shuttle has two opposite end faces and in which each of said buffers comprises a rigid housing which is open at least toward the shuttle, a resilient damping member contained in said housing and formed with a stop surface, and a resilient U-shaped member which is bulged toward said shuttle, said stop face being complementary to the associated end face of said shuttle.
 6. Reversing means as set forth in claim 5, in which each of said buffer housings comprises two spaced apart plates, which are connected by pins to form a cage in which said damping member is held.
 7. Reversing means as set forth in claim 6, in which said plates are formed with apertures and said damping member is adapted to extend through said apertures as it is deformed.
 8. Reversing means as set forth in claim 6, in which each of said damping members has a portion which is adjacent to the associated U-shaped member and spaced from at least one of said plates.
 9. Reversing means as set forth in claim 5, in which each buffer housing carries a roller, which protrudes toward the associated stressing arm and has an axis that is parallel to the axis of the associated torsion bar.
 10. Reversing means as set forth in claim 9, in which each of said stressing arms has at its free end a surface that is engageable by the associated roller and said engageable surface is inclined to the longitudinal direction of said race when the associated buffer engages the associated resilient stop under the force transmitted to said buffer by the associated torsion bar through the stressing arm connected thereto. 